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Home ‣ Electronics and Communication Engineering ‣ Microwave Communication See What Others Are Saying!
  • Question

  • Assertion (A): A backward wave oscillator has an internal positive feedback.

    Reason (R): A positive feedback is necessary for sustained oscillations.


  • Options
  • A. Both A and R are correct and R is correct explanation of A
  • B. Both A and R are correct but R is not correct explanation of A
  • C. A is correct but R is wrong
  • D. A is wrong but R is correct

  • Correct Answer
  • Both A and R are correct but R is not correct explanation of A 

    Explanation
    It is somewhat similar to TWT and can deliver microwave power over a wide frequency band.

    It has an electron gun and a helix structure. However the interaction between electron beam and RF wave is different than in TWT.

    The growing RF wave travels in opposite direction to the electron beam.

    The frequency of wave can be changed by changing the voltage which controls the beam velocity.

    Moreover the amplitude of oscillations can be decreased continuously to zero by changing the beam current.

    It features are:

    1. Frequency range - 1 GHz to 1000 GHz.

    2. Power output - 10 mV to 150 mW (continuous wave) 250kW (pulsed).

    It is used as signal source in transmitters and instruments.

    More questions

    • 1. In which region of a CE bipolar transistor is collector current almost constant?

    • Options
    • A. Saturation region
    • B. Active region
    • C. Breakdown region
    • D. Both saturation and active region
      • Discuss
    • 2. The Q factor of a waveguide resonator is given by (?0 is resonant frequency, U is energy storage and WL is the power loss)

    • Options
    • A.
    • B.
    • C. Q = ?0UWL
    • D.
      • Discuss
    • 3. In a resistance strain gauge, G = 2, stress = 1050 kg/cm2, R = 1000 ?. The value of ?R will be

    • Options
    • A. 2 ?
    • B. 3 ?
    • C. 4 ?
    • D. 1 ?
      • Discuss
    • 4. In a broadcast superheterodyne receiver

    • Options
    • A. the local oscillator operates below the signal frequency
    • B. local oscillator frequency is normally double the IF
    • C. RF amplifier normally works at kHz above the carrier frequency
    • D. mixer input must be tuned to the signal frequency
      • Discuss
    • 5. FM receivers using the standard 88 to 108 MHz band use IF of

    • Options
    • A. 8 MHz
    • B. 9.9 MHz
    • C. 10.7 MHz
    • D. 12.2 MHz
      • Discuss
    • 6. Which one of the following potential does not satisfy Laplace's equations?

    • Options
    • A. v = 10 xy
    • B. v = p cos ?
    • C.
    • D. v = f cos ? + 10
      • Discuss
    • 7. The rate at which information can be carried through a communication channel depends on

    • Options
    • A. carrier frequency
    • B. bandwidth
    • C. transmission loss
    • D. transmitted power
      • Discuss
    • 8. Generally the wall thickness of rectangular waveguide is

    • Options
    • A. about 1-5 mils
    • B. about 40-100 mils
    • C. about 0.1 to 0.5 mils
    • D. about 500 mils
      • Discuss
    • 9. It is known that noise phase modulates the FM wave. As the noise side band frequency approaches the carrier frequency, the noise amplitude

    • Options
    • A. will increase
    • B. will decrease
    • C. will remain constant
    • D. will reduce to negligible value
      • Discuss
    • 10. Curie Weiss law is .

    • Options
    • A. True
    • B. False
      • Discuss

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